Composite structure and the process of making the same



Patenta& Oct. 28, 1947 i i PROCESS OF MAKING THErSAME Seymour G. Saunders, Bloonfield Hills, and Harry Morrison, Detroit, Mici., assignors to -Chrysler Corporation, Highland 'Parlr, Micl a corporation of Delaware i v Application'october 17, 1944, Seriai No'.'5""59', 24 f4 (Ci. 154--130) i This invention'relates to an improved process of surface bonding together' parts of a composite structure and to an improved `bonded composite' structure, this application being a continuatiom' n-part of, and substitution for, our applications Serial Nos. 354230 and 447374, filed August 26.

i 1940, and June 17,1942, respectively.

' More particularly, the invention pertains to the provisior of an 'improved bond which is adapted* to'secure together parts co'mprising a wide variety o of materials including metal. wood,-p1astics, fiber. glass, ceramics and the like in any selectedcombinations.

Heretofore, vulcanized rubber in layers of .various thicknesses have been ecured to surfaces of 1 material of various kinds by initially treating the rubber surface to be attached with a cyclizing or isomerizing agent, such as sulphuricmacid, and then applying various t es of adhsives. in

these bonding procedures, strengths of the 'ref s ulting bonds have been. limited' by the reiatively low cohesion between the parti'cles of cyclized or isomerized rubber ofthe ,treatfd surface and the main vulcanized rubber ,body.' As a'result of this by separation of the cyclized surface film from the rubber body.

We have found that'the cohesionbetween the particles of cyclized rubber of such a surface film, i

of an intermediate yielding bonding layer that s 'over extended surface areas( of 'a water-proof bondlng strata between'iparts of a composite structure which comprises waterinsoluble material.

Other objec'ts 'of the invention are to provide in a jcomposite structure compri sing -rub-ber, a crazed bonding film consisting of cyclized rubber,

"the particles of which are 'tenaciously adhered together and to' the uncyclized body portion of the rubber; to provide in aprocess for bonding rubberto'divers'e materials the step of craz ing the cyclized'rubb'er film by flexure'in order to 'facilitat e penetratipi of thecem ent to the Junction' of the cyclized and 'u'ncyclized-rubber content andto provide in ahcompost e structure of this jkind a cement which is particularly'adapted to penetrat and bond togetherthe p`articles of the cyclized film in order to bond such film to the underlying uncyclizedrubber as well as to tenaciousl'y adhere to a'large variety "of materials.

` Another object of the invent on is the provision ina 'bondbetwen palrts of a composite structure adapted to accommodate, between such parts, controlled andresiliently opposed relative movecondition, bonds of theforegoing type have failed "ment of` suflicient amplitude to dissipate th imv pact of 'the -separatory and other forces applied thereon and to distribute the efiect of 'such forces A further' object oi" the invention is the proviand the rubber body, as well as the cohesionjof *sion of a bonding process' of thischaracter for 'the cyclized rubber particles to each other 'can be tremendously increased byvtheaus -of certain cement, hereinafter specified, and by' suitably manipulating the rubber layerfor body following the cyclizing treatment thereof in order to craze the treated sunfacefor admitting the cementto the junction of the cyclized ,film and the rubber body As far ascan be determined, such cement 'is capable 'of pen'etrating the cyclized rubber film and curing under beat and pressure whilein inti- 40 mate contact with both the cyclized rubber particles and the rubber body. v i

One of the mainobjects of the invention is the provision of a bonding process ,by whichparts I of a composite article can be secured together 46 with an ul-timatetensile strength of the order of 100o`tb 1200 pounds per .square inch without requiring in the; bonding operation compression of 'more than 15 to 25 pounds per square inch.

' Another objectpf the invention is the provision 50 sele'ctive" control' of' the yieldng properties -of the intermediate bonding layer betweenwide limits varying 7 "from i 'a substantially non-yielding rrg'id condition t'a' 'arelatively yielding state. A

Additional objects of the invention are to provide between bonded together bodiesan intermediate bonding lver which has a main body por tion comprising a', vulcanized rubber compound v -ber orequivalent synthetic rubber layer and to pr'ovide a cyclized rubber crust-like surface on the intermediate bndingjstrata 'ot a composit'e' structure whichablends by'decreasing cyclized' or c isomeriz'ed rubber. jcon centration into" the body or' the bonding" *sm-m; without' a"'sharp[or flabrupt line ofdem'arcation and'whichis accordingy 4 sointek rallyunited withth 'body partjcfjthe'bondmg' strataas:towithstahd'pdrting rrom the letter under st "sss less'than these required to part me shown'in the acc'o'npanyin'g drawings, oi' which: Fig.`1i s` a sectionalviewgdiagrammatically illusu tratin faj composite structur embodying 'the inventionghaving as one QS p'artj's'fia' ;body of ma- .terial` or `'syrthetti'c rubber-'like material which is' bon ded toa riid part or "el 'ment 'c'ompri'sing a;

'differentfimaterialg I Fig; `2 is' 'a a sectionaljview similar 'to Fig.: I dia;

ber 'bodies and a large variety o! materials. This' cement is particularly advantageous since it 'will penetrate the cyclized rubber films cohering the particles thereof together and to the uncyclized rubber content with great` tenacity while at the tive phenol formaldehyderesin. Modified poly- .vinyl acetateresin in solution in suitable solvents is available on the market under this nomenclature. It is a hydrolyzed polyvinyl ace- I tate having a complex chain of inter-linked molegrammatically illustratinga composite structure" v but havingtwo'parts' which comprise diverse nra- .terials bondedjtogether by an intermediate bonding layer embodying i this inventibn.

Fig; 3- is an enlarg' djragmentary sectional View of* ;the i bonding layer' shown' in mg, 2 and taken on the liirje il of'the latter figure; Fig. 4 is a 'fragmentary planv'iwoffan intermediate 'botiding layer having'. a crazed cyclied The improved?bonding'prccess compr'i'se's a pre'paratory treatment of `vulcanized rubber or equivalnt` syntheticrubber-like material in 'order 'rj' surface thereof to'be i tibnvan iribyzed rubber cqx'jcent'ratin ;nak um'vaue of substantiall'y purecy "d ubber at its ;exterior to'aminuteconcentr v the int erior of the rubber" body. This sacc'ompli'shediby the in'situs formati'onof "cyclid' rubber n* the vulcanized' rubber body or gii ana als'aresult; there is not' presenta-line f driarcation'between the. body part 'ofthefrubber enz me' cyclized rubber forma'- m iner, the attepgr i rubber body'under stresses less than those required to part portions of the rubber body itself. After the rubber body or sheet-like rubber V bonding layerhas been treatedji n the foregoing' sheet' in order toi-crackor Craze the cyclized` rubber film and 'thenapplying a suitable" cement either to the "isomrilzedfsurface;of the rubber' body or layer orto" the ;surfaceoith article to? bebonded' thereto.- The'solvent otthe cement is preferabiy eliminated by air dryi'fg or force dry ing in order to leave adeposit of unset'cernent and' the parts are assembledjin desired relati'on and' heated to the temperature' of 'the softning lyblends in decrease&- concntrat n" into he fody partijof the' rubber` thfus 'prjciviilrg*-` a substantially integral structure which` wiilfn'o't' separate or part from the' cules: The structure of the modified polymrmay be pictured as a long chain, the alternate links ofwhich are vinyl alcohol and vinyl acetate units:

-CH-CHrCH-CH -CH-CiirC -CHrococna H COCH: H

' In general, the actual distribution of the alcor hol and ester components in the chain depends on point of the cement which' varies"from 180 F. to

the chance hydrolysis of the ester group. The

exte'nt of hydrolysis'determines its water solubilityp Polyvinyl acetate which'has been hydrolized; as' indicated by the foregoing formula,` to an extent such that not more than substantially 50 mole per cent of the acetyl groups thereof havebeen replaced by hydroxyl groups is not water soluble. The waterresisting properties of v the ultimate bond arethus increased by the use* of acement comprising water-insoluble hydrolized poly"viny1 acetate resin and phenol formaldehyde resin. While polyvinyl acetate resin which has been hydrolized to 50 mole per cent is satisfactory;

such resins which have been hydrolized to an m; extent as low as 14 mole per cent are also satis'- factory; The'hydrolization of 'the' resin should be so limited a's not to `'convert it to a water soluble state.

The hydrolysis modified polyvinyl acetate resin v i maybe employed mixed in equal or any other' 'dsired p'roportions with heat reactive phenol' formaldehyde resin cement. Crazing of the cyclized rubber film greatly increases the coh'e sion' and 'adhesion resulting from the use 'of the above mentioned cement for the multiplicity' of cracks thus formed in the cyclized coating admits the cement to the junction of the cyclized and. uncyclized rubber portions. v

For the purpose of illustrating an' example, there is shown in Fig. 1 a layer of rigid material |0 which may comprise metal, wood, plastic, fiber, glass, ceramics, synthetic resin and the'like to which is bonded a body ll comprising vulcanized rubber. The surface I 2 :of the rubber body Il which is Secured to the member H)` is shownby stppling to have been isomerized by sulphuric acid or any other solution so as to pro duce a film |3 of cyclized rubber thereon and to have been crazed to produce a plurality of cracks I 2' therein. The crazed condition of the cyclized film as it appears prior to as sembly of the parts o fthe structure is illustrated in Fig. 4 in which the cracks produced by fiexure of the rubber sheet or body are designated by the numeral l2'. The side of the rubber body I I adjacent the memb'er` |0 is bonded to the latter member by a film M of set cement, the cement having penetrated the cyclized film and entered the Cracks thereof. In Fg. 2 of the drawings is illustrated a composite structure comprising two members l5 and IS each of whichmay comprise any of the above :nomer:

mentione'd materialsor' they` "n-ay com-prize they seine material; Theniembers-'tl nd l l are bond ed' together by intermediate'bondin Iyq IT of sheet-'like thickness comprisn 'vucanzed rubber.- 'the' oppdsite 'sides ot whch" have bean s'ubieot'ed to: anisomerizing action in orde' to product thereon in situs dormed v interaily con- ;marinar-ras is the cycized` rubber o! a' body of ngturarubber;

Although but several specific embodiments o! the invention are herein shown and described. it

wiliibe understood. thatvariou changes .in the equ e'nce ot Operations, stepsand material emnected mins of cyclize'd rubbe r. Thethusrtreated' sids of' the bonding layer'- 'IT are" a'dhered'to the adjacent sides' of the members`l5 and 'l'il by set\ filmslsgand [9 'of'the abovementionedacement.

As llustrate'd in the'. enlargedl'sectional 'view shown in-` Fig; 3; the concentration of cycized rubber a at the exte'rior of the' bonding layer' l' is much higher` than the` concentration ot.

oyclized'rubber in the'interior of the bndmg` layer.

erizatio'n of rubber. and' produces 'an integral' union 'between the exterior crust like' film' of subst'antia'lly pure cyc1ized'rubber .and the body of*` the vu lcanized'rubber sheet. consequentlmparting of "theblclizedr'bber film fr'om the vulcanized rubber bonding sheet-does' frot occur "un'der -stresses substantially g'r'ea ter than those "required This decreasihg of'. aconcentration of.` cyclizedfrubberinward'ly of theb'onding layer` results; it is believed; fromthe inz situsisom-- spirito! the inyention.:

wei claim n Aeomp'osite articleincluding a body of vul- 'poyed mayjbe made without' departingirom the canzed rubber andan adjacent second body, a

- modified polyvinyl acetate resin in which between to part the body of th'e rubbersheet. This gure also shows the' Cracks l z of th'er crazed' cycl'ized surface to be filled with setcement which securely coh'eres particles of 'thegset "film togetherand to'` the underlying rubber body.

In' theforegoing illustration of the improved bon'ing process, reference has been :made mainly' to' a 'bonding layer or body comprising. isomerized or cyclized'- 'a turail` rubber' compounds. Substantially equally satisfactory results may be'obtained' by using in the foregoing process, in place of 'natural rubber compou'n'ds; synthetic :rubberlike compounds such 'as neoprene, .which is .zpolymer-- ized `ch 1o"roprene, o`r Bunavrubber such as copoly- 'mer's of butad'ene andacrylic'hitrile or styrene in a' physicastate corresponding to vulcanized rubber. 'Bu'nairubber' may-:be :converted tonstate corresponding to Vuicanized "natural rubber :bya

used-in vuloanizingnatur'al rubber" while neoprene can be hardened to 'a' desi-red. degree :of yieldable firm'ness by polymerizingdt mth heat :and suit- `ab1e-po1ymerzing agents and polymeriza'tiom accelra-tor's. Inasmuch as both^of these. synthetic approxmately 14 and5'0 mole percent of the acetyl groups of the polyvinyl acetate resin have been replacedby hydroxyl groups and phenol formaldehyde resin..

2. .Inthe manufacturelof composite structures,

r including a vulcanized rubber member bonded to ar second-membenthe method of bonding parts of such structures together which comprises the steps of cyclizingthe 'surface of said rubber membler-to `be bonded to said second member by treatngsaid rubber surface. with sulphuric acid, flexing .said rubber member in order to Craze said cyclized surface, nd bonding said crazed cyclized surface ?to said secondu member while simultaneously bonding' the partcles of said crazed surface to each other and to `the interior uncyclized vucanizing action substantally ider'tcal to 'that 4 rubber compounds are available' on the open i market in' a statecorrespondingto that of -vul-- canized natural rubber, it'is notbelieved tobe necessary' to herein' set'forth:details of the'process by whichthey are' formed'and such products `are acc'rdingly, hereinand in the claims appended e hereto,`r`eferred-to as vulcanized synthetc rubber like materials, vulcanizedineoprene -andfvu-lcanizdBna rubber.

Surfaces of bodies'` or' sheets compri'sing syntheticrbber=1ike ,cm'po'undsof the above 'class 'may be 'preparedlfor-'bondirg by applyin'g th'ereon a 'y'clizing por ismerizin'g a'gent selected from 'the group consisting 'of 'sulphuric a'cii hydrochlo'ic a'c'i'd and prchioric acid in fi the "same marinar fas the surfaces 'of natural "rubber com- *pounds' and the "resulting ,cyclized formation. va-

'ries in cyclized content frma' maximum' concentration at the exterior of 'the surace'to a minimum concentration at the'interior ofth'eyieidable body or layer. The i Cyclzed synthet-ic: rubber like materiai is th'erefore integrallyunited with the yieldable body or` 'layer' without adistinct line'of' demarcatio'n, much in the' same portion of said ;rubber member by heat curlng under'pressure between said cyclized rubber film and saidsecond membera cement comprising a 'mixture of water-insoluble hydrolysis modified polyvinyl acetate `resinin which between approximately 14 and 50 mole percent of the acetyl groupso'f the polyvinyl acetate resin have been 'replaced by hydroxyl groups and phenol form- I aidhyde resin cem'ents:

.3. Acompositearticle'including a body of 'cured rubber-likemater'al andan adjacent second body,

a crazedmm comprisingsaid rubber-like material in cyc'lized state on the surface of said rubber-like bodyadjacent said second body, and a. set film of cementbetween and bonded to said second body and said cyclized film having integral portions .penetrating thelatter for bonding the particles of saidcrazed'cyclized film to each other and to the un'cyclized rubber-like material 'adjacent said cyclized' iflmand comprsing a mixture of waterinsoluble .hydrolysis modified polyvinyl acetate resin=in*which' between approximately 14 and 50 moiebercentofthe acetyl groupsof .the polyvnyl ua-cetate resin have :been replaced by hydroxyl groupsandrra phenol .formaldehyde resin.

'4. In-the'manufacture of 'composite structures, includinga cured-rubber-like member bonded to '-a-:.second:member, the' method of bonding parts of' such structures together which'comprises the :steps of :cyclizing'the surface of said rubber-like member to be bonded' to said second member by .treatingsaid surfacewith sulphuric acid, flexing said."rubber like memberin order to craze said cyclizedxsurfacmand bonding said crazed cyclized surfaceto saidsecond member while simultaneously` bonding thepa rticles of said crazed surface to eachother and to the interier uncyclized portion of1-said-rubber-like..member by applying e 8 on said cyclized surface and the, surface to which I 1 s r j it is to be bonded a resin cement having a. volatile REFERENCES CITED vehicle and comprising a mxture of water-im I Th following r erences are of record inthe sluble hydrolysis modified polyvinyl acetalte resin file of this patent: in which between approximately 4 and 5 0 mole ;5 r UNITED STATES PAm's percent of the acety groups of the polyviny] acez tate resin have been replaced by {hydroxy groups Number m I 'Date and a phenol formaldehyde res'n, removing the 3 n s r 93 volatle vehicle from said cement coated surfaces, 2341393 t en &1944 and heat curing the resulting dred cement while 10 260341 OQWa y 4, 1832 said surfaces are held together under press ure. t 2378311 M 27, 1937 SEYMOUR G. SAUNDERS. o y-- u Mar. 15, 1938 'HARRY MORRISON. t e 

